Wireless power transmission device and wireless power transmission system

ABSTRACT

A wireless power transmission device that transmits wireless power by a radio wave to a plurality of power receivers, has a power transmission condition calculator that calculates power transmission conditions including power transmission periods of two or more of a plurality of different power transmission patterns based on receiving power information and required electric energy information from the plurality of power receivers, and power transmission circuitry that transmits a radio wave while switching between the two or more power transmission patterns under the calculated power transmission conditions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2018-19372 filed on Feb. 6,2018 and No. 2019-720 filed on Jan. 7, 2019, the entire contents ofwhich are incorporated herein by reference.

FIELD

Embodiments of the present invention relate to a wireless powertransmission device and a wireless power transmission system.

BACKGROUND

There is known a technique for transmitting radio waves based on aplurality of antenna patterns from a power transmitter, notifies by apower receiver the ID of the antenna pattern in which the maximumreceiving power was obtained by the power receiver to the powertransmitter, and transmitting power based on the notified antennapattern.

In addition, there is also known a technique for optimizing thedistribution of power transmission pulses to be transmitted to aplurality of power receivers according to battery demands of the powerreceivers and transmitting the transmission pulses to the individualpower receivers.

However, even though a power transmission pulse is distributed to aspecific target power receiver, the radio wave including the powertransmission pulse is spatially diffused and received by other powerreceivers. In fact, there has not been conventionally suggested anymethod for optimal power distribution that takes this matter intoconsideration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a schematic configuration of awireless power transmission system including wireless power transmissiondevices according to a first embodiment;

FIG. 2 is a block diagram illustrating an example of an internalconfiguration of a power transmitter;

FIG. 3 is a block diagram illustrating an example of an internalconfiguration of a power receiver;

FIG. 4 is a block diagram of the power transmitter illustrating amodification example of FIG. 2;

FIG. 5 is a block diagram of the power receiver illustrating amodification example of FIG. 3;

FIG. 6 is a flowchart illustrating an example of a procedure for a batchfeedback method;

FIG. 7 is a timing chart for the batch feedback method;

FIG. 8 is a flowchart illustrating an example of a procedure for asequential feedback method;

FIG. 9 is a timing chart for the sequential feedback method;

FIG. 10 is a diagram illustrating an example of a receiving power tablethat provides a summary of receiving power information and requiredelectric energy information received by the power transmitter from thepower receivers;

FIG. 11 is a diagram illustrating how to determine the optimum solutionto a linear programming problem;

FIG. 12 is a diagram illustrating respective receiving powercharacteristics and receiving electric energy characteristics of thepower receivers;

FIG. 13A is a diagram illustrating an example of radio wave transmissionin numerical order, and FIG. 13B is a diagram illustrating an example ofradio wave transmission in arbitrary order;

FIG. 14 is a block diagram illustrating a schematic configuration of awireless power transmission device according to a second embodiment;

FIG. 15 is a diagram illustrating the direction and beam width of powertransmission patterns and the installation locations of power receivers;and

FIG. 16 is a flowchart illustrating a procedure for a power transmitteraccording to the second embodiment.

DETAILED DESCRIPTION

According to one embodiment, a wireless power transmission device thattransmits wireless power by a radio wave to a plurality of powerreceivers, has a power transmission condition calculator that calculatespower transmission conditions including power transmission periods oftwo or more of a plurality of different power transmission patternsbased on receiving power information and required electric energyinformation from the plurality of power receivers, and powertransmission circuitry that transmits a radio wave while switchingbetween the two or more power transmission patterns under the calculatedpower transmission conditions.

Embodiments will be described below with reference to the drawings. Forthe ease of understanding and the convenience of illustration, some ofcomponents are omitted or described and illustrated in a modified orsimplified manner in this specification and the attached drawings.However, the embodiments are to be interpreted including technicalmatter that can be expected to perform similar functions. For theconvenience of illustration and the ease of understanding, the reductionscales and the length-to-width ratios are modified and exaggerated asappropriate in the drawings attached to this specification.

First Embodiment

FIG. 1 is a block diagram illustrating a schematic configuration of awireless power transmission system 2 including wireless powertransmission devices 1 according to a first embodiment. The wirelesspower transmission system 2 illustrated in FIG. 1 includes one or morepower transmitters 3 and a plurality of power receivers 4. When thereare two or more power transmitters 3, the power transmitters 3 transmitor receive information to or from each other in a wireless or wiredmanner to generate a plurality of power transmission patterns 5 incooperation. Radio waves based on two or more of the power transmissionpatterns 5 generated by the one or more power transmitters 3 aretransmitted to the plurality of power receivers 4. More specifically,the one or more power transmitters 3 transmit radio waves whileswitching in sequence between the two or more of the power transmissionpatterns 5. Each of the power transmission patterns 5 is transmitted inits specific transmission periods. Each of the power receivers 4receives the foregoing radio waves transmitted from the one or morepower transmitters 3 and generates direct-current power. The wirelesspower transmission device 1 illustrated in FIG. 1 is a collective termof the power transmitter 3 and the power receiver 4. In some cases, theone or more power transmitters 3 may transmit radio waves based on onlyone power transmission pattern 5. However, mainly in the exampledescribed below, the one or more power transmitters 3 transmit radiowaves based on two or more of the power transmission patterns 5 whileswitching.

FIG. 2 is a block diagram illustrating an example of an internalconfiguration of a power transmitter 3. The power transmitter 3illustrated in FIG. 2 has a power transmission antenna 11, a firstcommunication antenna 12, a power transmission unit (power transmissioncircuitry) 13, a first communication unit (first communicator) 14, afirst control unit (first controller) 15, a first storage unit 16, and afirst calculation unit (first calculator) 17.

The power transmission unit 13 performs trial power transmission andactual power transmission. In the trial power transmission, the powertransmission unit 13 transmits radio waves based on a plurality of powertransmission patterns 5 at different timings. In the actual powertransmission, the power transmission unit 13 transmits radio waves whileswitching between two or more of the power transmission patterns 5,based on the receiving power information and required electric energyinformation from the plurality of power receivers 4.

The first communication unit 14 is not intended to transmit wirelesspower but transmits or receives various kinds of information to or fromthe plurality of power receivers 4. For example, the first communicationunit 14 receives the receiving power information and the requiredelectric energy information transmitted by the plurality of powerreceivers 4.

The first calculation unit 17 calculates power transmission conditionsincluding respective power transmission periods of the two or more ofthe power transmission patterns 5, based on the receiving powerinformation and the required electric energy information from theplurality of power receivers 4. The power transmission conditionscalculated by the first calculation unit 17 may include not only thepower transmission periods of the power transmission patterns 5 but alsoa parameter including at least one of the directions of the two or morepower transmission patterns 5, the phases of the radio waves, and theamplitudes of the radio waves.

The first storage unit 16 stores the power transmission conditionscalculated by the first calculation unit 17 and others. For example, thefirst storage unit 16 stores the power transmission periods of the powertransmission patterns 5 and the parameter described above, and others.In addition, the first storage unit 16 may store the receiving powerinformation and required electric energy information from the pluralityof power receivers 4.

The first control unit 15 controls the respective portions of the powertransmission unit 13. For example, the first control unit 15 performscontrol for transmitting the receiving power information and requiredelectric energy information received by the first communication unit 14to the first calculation unit 17 and control for transmitting the powertransmission conditions calculated by the first calculation unit 17 tothe power transmission unit 13. The first control unit 15 also controlswriting of various kinds of information into the first storage unit 16and controls reading of various kinds of information from the firststorage unit 16.

When the plurality of power transmitters 3 is provided, the powertransmitters 3 may share the first communication antenna 12, the firstcommunication unit 14, the first control unit 15, the first calculationunit 17, and a power signal source not illustrated. This makes itpossible to simplify the respective internal configurations of the powertransmitters 3.

FIG. 3 is a block diagram illustrating an example of an internalconfiguration of the power receiver 4. The power receiver 4 illustratedin FIG. 3 has a power receiving antenna 21, a second communicationantenna 22, a power reception unit (power reception circuitry) 23, ameasurement unit 24, a second communication unit (second communicator)25, a second control unit (second controller) 26, a second storage unit27, and a second calculation unit (second calculator) 28.

The power reception unit 23 receives radio waves from the one or morepower transmitters 3 and generates direct-current power. The powerreception unit 23 has a rectifier 23 a and a load 23 b. The rectifier 23a converts received alternating-current power into direct-current power.The measurement unit 24 measures the receiving power defined by theamplitude of the direct-current power at the load 23 b. Besides, thepower reception unit 23 may have a matching device and a DC-DCconverter. The matching device performs impedance matching between thepower receiving antenna 21 and the rectifier 23 a. The DC-DC convertertransforms the voltage after the rectification.

The second communication unit 25 transmits or receives various kinds ofinformation to or from the one or more power transmitters 3 via thesecond communication antenna 22. For example, the second communicationunit 25 transmits to the one or more power transmitters 3 theinformation of the receiving power by the radio waves based on theplurality of power transmission patterns 5 and required electric energyinformation. The second storage unit 27 calculates the required electricenergy information of the power receivers 4. The required electricenergy information is calculated based on the charging states and powerconsumptions of the power receivers 4. The second storage unit 27 storesthe receiving power information, the required electric energyinformation, and others. The second control unit 26 controls therespective portions of the power reception unit 23.

FIG. 4 is a block diagram of the power transmitter 3 illustrating amodification example of FIG. 2, and FIG. 5 is a block diagram of thepower receiver 4 illustrating a modification example of FIG. 3. Thepower transmitter 3 illustrated in FIG. 2 and the power receiver 4illustrated in FIG. 3 are internally configured not to estimate apropagation path. However, the power transmitter 3 illustrated in FIG. 4and the power receiver 4 illustrated in FIG. 5 are internally configuredto estimate a propagation path. The propagation path refers to apropagation path between the power transmitter 3 and each of the powerreceivers 4.

The power transmitter 3 illustrated in FIG. 4 has the same internalconfiguration as the power transmitter 3 illustrated in FIG. 2, andfurther includes a propagation path estimation unit (propagation pathestimator) 18 and a first transmission/reception switch 19. Thepropagation path estimation unit 18 receives a beacon signal from thepower receiver 4 and estimates the propagation path to the powerreceiver 4 based on the received beacon signal. The firsttransmission/reception switch 19 switches transmission and receptionmodes for the transmission of the radio waves and the estimation of thepropagation path, respectively.

The power receiver 4 illustrated in FIG. 5 has the same internalconfiguration as the power receiver 4 illustrated in FIG. 3 and furtherincludes a beacon signal transmission unit 29 and a secondtransmission/reception switch 30. The beacon signal transmission unit 29transmits a beacon signal at the time of estimation of the propagationpath. The second transmission/reception switch 30 switches transmissionand reception modes for the transmission of the beacon signal for theestimation of the propagation path and the reception of radio waves fromthe one or more power transmitters 3, respectively.

As described above, the power transmitter 3 performs trial powertransmission and actual power transmission. As methods for trial powertransmission, there are batch feedback method and sequential feedbackmethod. In the batch feedback method, the power transmitter 3 transmitscontinuously radio waves based on the plurality of power transmissionpatterns 5, and then receives collectively the receiving powerinformation and required electric energy information from the pluralityof power receivers 4. On the other hand, in the sequential feedbackmethod, at each time of transmission of radio waves based on theindividual power transmission patterns 5, the receiving powerinformation and required electric energy information are received fromthe plurality of power receivers 4.

FIG. 6 is a flowchart illustrating an example of a procedure for thebatch feedback method, and FIG. 7 is a timing chart for the batchfeedback method. The flowchart in FIG. 6 illustrates the procedure forprocessing by the one or more power transmitters 3. In steps S1 to S4 ofFIG. 6, the power transmitter 3 performs continuously the trial powertransmission of the radio waves based on the plurality of powertransmission patterns 5. More specifically, first, a variable kindicating the kind of the power transmission pattern 5 is initializedto zero (step S1). Next, k is incremented by one (step S2). Then, thepower transmitter 3 performs the trial power transmission of the radiowave based on the k-th power transmission pattern 5 (step S3). Then, thepower transmitter 3 determines whether the variable k has reachedmaximum value K (step S4). When the variable k has not yet reached themaximum value K, the power transmitter 3 repeats step S2 and subsequentsteps. Accordingly, as illustrated at times t1 to t2 illustrated in FIG.7, the radio waves based on the plurality of power transmission patterns5 is continuously transmitted. The transmission periods of the powertransmission patterns 5 during the trial power transmission can be setarbitrarily. Each of the power receivers 4 receives the radio wave basedon the power transmission patterns 5 and stores the receiving powerinformation in the second storage unit 27.

When it is determined in step S4 that the variable k has reached K, eachof the power receivers 4 transmits the receiving power information andthe required electric energy information as illustrated at times t3 tot4 in FIG. 7. Each of the power transmitters 3 receives the receivingpower information and the required electric energy informationtransmitted by each of the power receivers 4, and stores theirinformation in the first storage unit 16 (step S5). The order in winchthe plurality of power receivers 4 transmits the receiving powerinformation and the required electric energy information can be setarbitrarily. In addition, the plurality of power receivers 4 maymodulate the receiving power information and the required electricenergy information at different frequency bands before transmission.

Next, the first calculation unit 17 calculates the transmission periodsof the two or more power transmission patterns 5 based on the receivingpower information and required electric energy information (step S6 inFIG. 6 and times t5 to t6 in FIG. 7). At this time, the firstcalculation unit may also calculate various parameters other than thetransmission periods.

Next, based on the results of the calculation in step S6, the powertransmitter 3 performs the actual power transmission while switchingbetween the two or more power transmission patterns 5 (step S7 in FIG. 6and times t7 to t8 in FIG. 7). Accordingly, the power transmissionpatterns 5 of the power transmitter 3 are switched in each of thespecific transmission periods (times t7 to t8 in FIG. 7). The one ormore power transmitters 3 transmits the radio waves while switchingbetween the transmission periods of the power transmission patterns 5based on the receiving power information and the required electricenergy information from the power receivers 4. Each of the powerreceivers 4 may monitor whether the radio waves from the actual powertransmission have been received by the measurement unit 24 and providethe power transmitters 3 with information indicative of the monitoringresults on a regular basis.

FIG. 8 is a flowchart illustrating an example of a procedure for thesequential feedback method, and FIG. 9 is a timing chart for thesequential feedback method. The flowchart in FIG. 8 illustrates theprocedure for processing by the one or more power transmitters 3. StepsS11 to S13 are similar to steps S1 to S3 in FIG. 6. After performing thetrial power transmission of the radio wave based on the k-th powertransmission pattern 5 in step S13, the power transmitter 3 receives thereceiving power information and the required electric energy informationfrom the power receivers 4 having received the radio wave (step S14).The power transmitter 3 stores the received receiving power informationand required electric energy information in the first storage unit 16.For example, times t11 to t12 in FIG. 9 corresponds to the trial powertransmission period of the radio wave based on the first powertransmission pattern 5, and times t13 to t14 corresponds to the periodof reception of the receiving power information and the requiredelectric energy information from the power receivers 4 having receivedthe radio wave.

Next, the power transmitter 3 determines whether the variable k hasreached K (step S15). When the variable k has not reached, the powertransmitter 3 repeats step S12 and subsequent steps. When determining instep S15 that the variable k has reached K, the power transmitter 3reads collectively the receiving power information corresponding to thepower transmission patterns 5 and the required electric energyinformation from the first storage unit 16, and the first calculationunit 17 calculates the transmission periods of the two or more powertransmission patterns 5 (step S16 in FIG. 8 and times t15 to t16 in FIG.9). Next, based on the results of calculation in step S6, the powertransmitter 3 performs the actual power transmission while switchingbetween the two or more power transmission patterns 5 (step S17 in FIG.8 and times t17 to t18 in FIG. 9).

In this way, in the batch feedback method, each of the power receivers 4transmits collectively the information of the receiving power by theradio waves based on the plurality of power transmission patterns 5 andthe required electric energy information to each of the powertransmitters 3. Accordingly, each of the power transmitters 3 canreceive collectively the receiving power information and the requiredelectric energy information, and calculate the transmission periods ofthe power transmission patterns 5 immediately after the reception. Onthe other hand, in the sequential feedback method, each of the powerreceivers 4 transmits the information of the receiving power by theradio wave based on the power transmission patterns 5 and the requiredelectric energy information to each of the power transmitters 3 atindividual timings. Accordingly, each of the power transmitters 3 storessequentially the receiving power information and the required electricenergy information in the first storage unit 16 until all theinformation is received. After reception of all the receiving powerinformation and the required electric energy information, the powertransmitter 3 calculates the transmission periods and parameters of thepower transmission patterns 5.

FIG. 10 is a diagram illustrating an example of a receiving power table6 that provides a summary of receiving power information and requiredelectric energy information received by the power transmitter 3 from thepower receivers 4. This table is stored in the first storage unit 16. Inthe receiving power table 6 in FIG. 10, the identification numbers ofthe power receivers 4 are indicated in rows, and the identificationnumbers of the radio waves based on the power transmission patterns 5are indicated in columns. The cells in the rows and columns record thecorresponding receiving power. The cells in the last row record thetransmission periods of the power transmission patterns 5 calculated bythe first calculation unit 17. The cells in the last column record therequired electric energies of the power receivers 4.

The first control unit 15 and the power transmission unit 13 in each ofthe power transmitters 3 perform actual power transmission withreference to the receiving power table 6 in FIG. 10.

Next, a method for calculating the transmission periods of the powertransmission patterns 5 by the first calculation unit 17 will bedescribed. When the transmission period of the actual power transmissionbased on the k-th power transmission pattern 5 is defined as t_(k), thetotal time T in which power transmission based on the total K powertransmission patterns 5 is expressed in the following equation (1):

$\begin{matrix}{T = {{\sum\limits_{k = 1}^{K}t_{k}} = {t_{1} + t_{2} + \ldots + t_{K}}}} & (1)\end{matrix}$

where the time t_(k) is a non-negative real number and thus

t_(k)≥0   (2).

Next, based on the receiving power table 6 in FIG. 10, the receivingpower of the n-th power receiver 4 at the time of the trial powertransmission of the k-th power transmission pattern 5 is defined asp_(n,k). In order for the electric energy of the n-th power receiver 4to meet required electric energy W_(n), it is necessary to determine thetransmission period t_(k) satisfying the following equation (3):

$\begin{matrix}{{\sum\limits_{k = 1}^{K}{p_{n,k}t_{k}}} = {{{p_{n,1}t_{1}} + {p_{n,2}t_{2}} + \ldots + {p_{n,K}t_{K}}} \geq W_{n}}} & (3)\end{matrix}$

In the equation (3), when p_(n,k) is not zero, setting the transmissionperiod t_(k) to a large value would finally satisfy the requiredelectric energy W_(n). However, from the viewpoints of power saving andshortening the transmission period, the transmission period t_(k), thatis, the total time T is desirably as shorter as possible. Therefore, tosatisfy the required electric energies of all the power receivers 4 inthe shortest time, the minimization problem in the following equation(4) for the transmission period t_(k) needs to be solved:

$\begin{matrix}{{{{{Minimize}\mspace{20mu} T} = {t_{1} + t_{2} + \ldots + t_{K}}}{s.t.\mspace{14mu} t_{1}},t_{2},\ldots \mspace{14mu},{t_{K} \geq 0}}{{{p_{1,1}t_{1}} + {p_{1,2}t_{2}} + \ldots + {p_{1,K}t_{K}}} \geq W_{1}}{{{p_{2,1}t_{1}} + {p_{2,2}t_{2}} + \ldots + {p_{2,K}t_{K}}} \geq W_{2}}\mspace{56mu} \ldots {{{p_{N,1}t_{1}} + {p_{N,2}t_{2}} + \ldots + {p_{N,K}t_{K}}} \geq W_{N}}} & (4)\end{matrix}$

As seen from the equation (4), the minimization problem in the equation(4) is a linear programming problem in which both an objective functionand a constraint are expressed in linear form. FIG. 11 is a diagramillustrating how to find the optimum solution to a linear programmingproblem. FIG. 11 illustrates an example in which the number of powertransmission patterns 5 is two and the number of the power receivers 4is two. The shaded part in the drawing represents a feasible regionwhere the constraint is satisfied. In a linear programming problem, theoptimum solution exists at a vertex of a polygon representing a feasibleregion.

In the case of FIG. 11, when the objective function of the total time Tindicated by a broken line is approached asymptotically to the originpoint, the vertex (t₁′, t₂′) is the optimum solution where the totaltime T is the shortest. When the number of the power transmissionpatterns 5 is two and the number of the power receivers 4 is two, theoptimum solution can be easily searched for in graph form as illustratedin FIG. 11. However, when the number of the power transmission patterns5, that is, the variable is 3 or more, the feasible region is expressedin a polytope, and it is very difficult to determine the optimumsolution by intuition. In this case, a global optimum can be efficientlyfound out by checking vertexes in the feasible region based on aspecific rule using a simplex method. FIG. 12 illustrates the receivingpower characteristics of the power receivers 4 with respect to time inthe upper part and the receiving electric energy characteristics of thepower receivers 4 with respect to time in the lower part, in the casewhere actual power transmission is performed based on the results ofcalculation by the first calculation unit 17.

As for the receiving power characteristics in the upper part of FIG. 12,when there is no fluctuation in the radio wave propagation environmentand the positions of the power receivers 4, the receiving power duringtransmission of the radio wave based on the same power transmissionpattern 5 is constant. When the switching of the power transmissionpatterns 5 takes place, the receiving power varies depending on thepower transmission pattern 5.

As for the receiving electric energy characteristics in the lower partof FIG. 12, the gradients in the graphs of the receiving electricenergies with respect to time are constant during the transmission ofthe radio wave based on the same power transmission pattern 5. When thepower transmission patterns 5 are switched, the gradients in the graphsof the receiving electric energies vary. The broken lines in the lowerpart of FIG. 12 indicate the required electric energies. Thetransmission periods of the power transmission patterns 5 are set suchthat, upon transmission of the radio wave based on the last K-th powertransmission pattern 5, the receiving electric energies of the all powerreceivers 4 reach or exceed the broken line levels.

FIG. 12 illustrates an example in which the radio waves based on thepower transmission patterns 5 are transmitted in numerical order fromthe first power transmission pattern 5 to the K-th power transmissionpattern 5. However, the power transmission patterns 5 may be transmittedin arbitrary order. FIG. 13A illustrates an example of transmission ofradio waves based on the power transmission patterns 5 in numericalorder, and FIG. 13B illustrates an example of transmission of radiowaves based on the power transmission patterns 5 in arbitrary order. Theradio waves based on the power transmission patterns 5 do notnecessarily need to be collectively transmitted but each of the powertransmission patterns 5 may be divided by a plurality of transmissionperiods so that the divided power transmission patterns 5 aretransmitted in arbitrary power transmission order as illustrated in FIG.13B.

(First Modification)

The radio wave is desirably transmitted from the one or more powertransmitters 3 to the plurality of power receivers 4 in as short time aspossible. Specifically, the radio waves are desirably transmitted fromeach of the power transmitters 3 to the plurality of power receivers 4while switching between the two or more power transmission patterns 5such that the required electric energy of the power receivers 4 can besatisfied within a predetermined time. As methods for setting thepredetermined time, there are a first method and a second method asdescribed below.

In the first method, when all K power transmission patterns 5 aretransmitted in an equal power transmission period t_(equal), a minimumtime T_(1,min) needed to meet the required electric energies of all Npower receivers 4 is the predetermined time. When the total time isdefined as T1, the transmission period t_(equal) equally allocated toall the K power transmission patterns 5 is expressed by the followingequation (5):

$\begin{matrix}{t_{equal} = \frac{T_{1}}{K}} & (5)\end{matrix}$

According to the foregoing equation (3), when the power transmissionpatterns 5 are transmitted in the equal transmission period t_(equal),the receiving electric energy of the n-th power receiver 4 is expressedby the left-hand side of the equation (6) shown below. The receivingelectric energy needs to be equal to or larger than required electricenergy W_(n) of the n-th power receiver 4 expressed by the right-handside of the equation (6):

$\begin{matrix}{{t_{equal}{\sum\limits_{k = 1}^{K}p_{n,k}}} \geq W_{n}} & (6)\end{matrix}$

Therefore, the minimum time T_(1,min) for meeting all the requiredelectric energies of all the N power receivers 4 is expressed by thefollowing equation (7):

$\begin{matrix}{T_{1,\min} = {K\; {\max( {\frac{W_{1}}{\sum\limits_{k = 1}^{K}p_{1,k}}\frac{W_{2}}{\sum\limits_{k = 1}^{K}p_{2,k}}\mspace{14mu} \ldots \mspace{14mu} \frac{W_{N}}{\sum\limits_{k = 1}^{K}p_{N,k}}} )}}} & (7)\end{matrix}$

The term max( ) in the equation (7) indicates the maximum value of thevector in ( ).

In the second method, the predetermined time is defined as the minimumtime T_(2,min) to satisfy the required electric energies of the all Npower receivers 4 under the assumption that each of the power receivers4 feedbacks the information of the receiving power only by the powertransmission pattern 5 which yields the maximum receiving power at therespective power receiver 4 to the power transmitter 3.

When a maximum receiving power p_(n,k) has been obtained from the k-thpower transmission pattern 5 in the n-th power receiver 4, the shortesttime t_(n,k) satisfying the required electric energy W_(n) of the n-thpower receiver 4 is determined by the following equation (8):

$\begin{matrix}{t_{n,k} = \frac{W_{n}}{p_{n,k}}} & (8)\end{matrix}$

In the case that the maximum receiving power has been obtained by thek-th power transmission pattern 5 in two or more of the plurality ofpower receivers 4, the transmission period t_(k,min) of the k-th powertransmission pattern 5 is set to the longest one of the minimum timest_(n,k) satisfying the required electric energies of the correspondingpower receivers calculated in the equation (8). As for the powertransmission pattern 5 not selected by any of the power receivers 4, thetime t_(k,min) is set to zero and this power transmission pattern 5 isnot used in the actual power transmission. According to the foregoingequation (3), the receiving electric energy of the n-th power receiver 4in the case of transmitting the k-th power transmission pattern 5 in thetransmission period t_(k,min) is expressed by the left-hand side of theequation (9) shown below. The receiving electric energy needs to beequal to or larger than the required electric energy W_(n) of the n-thpower receiver 4 expressed by the right-hand side of the equation (9):

$\begin{matrix}{{\sum\limits_{k = 1}^{K}{p_{n,k}t_{k,\min}}} \geq W_{n}} & (9)\end{matrix}$

In the above, the transmission period t_(k,min) of the k-th powertransmission pattern 5 is defined in advance to meet the requiredelectric energies W_(n) of all the power receivers 4. Accordingly, inactuality, the value of the left-hand side of the equation (9) could beexcessively larger than the value of the right-hand side of the equation(9). Therefore, a scale factor s_(n) is introduced and defined by thefollowing equation (10):

$\begin{matrix}{s_{n} = \frac{\sum\limits_{k = 1}^{K}{p_{n,k}t_{k,\min}}}{W_{n}}} & (10)\end{matrix}$

Minimum value s_(min) of the scale factor s_(n) to all the powerreceivers 4 is expressed by the following equation (11):

s _(min)=min(s ₁ , s ₂ , . . . , s _(N))   (11)

The term min( ) in the equation (11) indicates the minimum value of thevector in ( ). Specifically, the transmission period t_(k,min) of thek-th power transmission pattern 5 is divided by the minimum scale factors_(min) to determine a total minimum time T_(2,min) satisfying therequired electric energies W_(n) of all the power receivers 4. From theforegoing matter, the minimum time T_(2,min) is expressed by thefollowing equation (12):

$\begin{matrix}{T_{2,\min} = \frac{\sum\limits_{k = 1}^{K}t_{k,\min}}{s_{\min}}} & (12)\end{matrix}$

(Second Modification)

The power transmission antenna 11 of the power transmitter 3 may be aphased array antenna. The phased array antenna has a plurality ofantenna elements and a variable phase shifter connected to these antennaelements. The variable phase shifter can control the phases of radiowaves input into the antenna elements to generate arbitrary powertransmission patterns 5. The phased array antenna may have a variableamplifier in addition to the variable phase shifter. Providing avariable amplifier makes it possible to control the amplitudes of radiowaves and suppress radiation of power in unnecessary directions, therebyallowing generation of power transmission patterns 5 with higher degreesof freedom.

(Third Modification)

Radio waves for use in power transmission are desirably non-modulatedcontinuous waves from the viewpoints of improving the power transmissionefficiency and reducing interference with other wireless facilities. Inaddition, the radio waves for use in power transmission and the radiowaves for use in communications are desirably different in frequency soas not to hinder communications between the power receivers 4. Thisallows power transmission from the power transmitters 3 and transmissionof the receiving power information from the power receivers 4simultaneously without interference.

(Fourth Modification)

The method for controlling the transmission periods assigned to theplurality of prepared power transmission patterns 5 has been describedso far. However, the power transmission patterns 5 may be variablycontrolled.

For example, like the power transmitter 3 illustrated in FIG. 4 and thepower receiver 4 illustrated in FIG. 5, the power transmission patterns5 may be decided based on the propagation path information between thepower transmitter 3 and the power receiver 4. More specifically,singular vectors on the power transmission side obtained by singularvalue decomposition of a propagation path matrix between the pluralityof power transmitters 3 and the plurality of power receivers 4 areequivalent to phase and amplitude information of radio waves input intothe power transmission antennas of the power transmitters 3(hereinafter, called weights). In particular, the weight correspondingto the maximum singular value generates the power transmission pattern 5by which the sum of alternating-current power received by all the powerreceivers 4 is maximized. However, this weight may not maximize the sumof direct-current power received by all the power receivers 4 due tonon-linearity of rectification efficiency of the rectifiers 23 a of thepower receivers 4. In addition, the weights corresponding to thenon-zero singular values are capable of supplying power to the powerreceivers 4 but the weights corresponding to the zero singular valuesare not capable of supplying power. Therefore, the weights correspondingto the zero singular value should not be used for power transmissionpatterns 5. One or more of the weights corresponding to the non-zerosingular values can be used as power transmission patterns 5.

Moreover, in order to concentrate a transmission power to one specificpower receiver 4, the weight given as a complex conjugate of apropagation path vector for this power receiver 4 can be used. Thismethod is widely known as retro-directive method. Therefore, one or moreof the retro-directive weights for the respective power receivers 4 canbe used as power transmission patterns 5.

The foregoing weights may not be strictly reproduced depending on theresolutions of the variable phase shifter and the variable amplifier andthe dynamic range of the variable amplifier. In this case, pseudoweights that are rounded to settable phase values or amplitude valuesclose to ideal weights or in which the upper and lower limits of theamplitude are clipped or compressed to fall within the dynamic range canbe used.

(Fifth Modification)

When none of the power transmitters 3 and the power receivers 4 has apropagation path estimation function as the power transmitter 3illustrated in FIG. 2 and the power receiver 4 illustrated in FIG. 3, itis difficult to determine the power transmission patterns 5 based on thepropagation path information described above in relation to the fourthmodification. Instead of deciding the power transmission patterns 5 fromthe propagation path information, the power transmission patterns 5 canbe decided based on relative position or direction information of thepower receivers 4 to the power transmitters 3. For example, in in-doorenvironments such as commercial facilities and factories, surveillancecameras or the like (power receiver localization units) are arranged sothat the location information of the power receivers 4 can be obtainedfrom image information provided by the cameras. In outdoors, thelocations of the power receivers 4 can be roughly specified by the GPS.Besides, a radar or the like separately installed on the transmissionside can receive signals used for communication by the power receivingside to acquire the location information.

With a phased array consisting of the power transmission antennas 11arranged one-dimensionally or two-dimensionally at equal spaces, thetraveling direction of the wave front can be controlled by givingappropriate phase differences to the radio waves input into the powertransmission antennas 11 and transmission power can be concentrated to aspecific direction. In this way, one or more power transmission patterns5 based on the location or direction information can be used for thepower receivers 4 without a propagation path estimation function.

In this way, in the present embodiment, based on the receiving powerinformation and the required electric energy information from theplurality of power receivers 4, the transmission periods of the two ormore power transmission patterns 5 are calculated, and these powertransmission patterns 5 are transmitted while switching between thecalculated transmission periods. This makes it possible to transmitradio waves meeting the required electric energies from the plurality ofpower receivers 4. In the present embodiment, the power transmitter 3performs trial power transmission and actual power transmission. In thetrial power transmission, the radio waves based on the plurality ofpower transmission patterns 5 are continuously transmitted, and theplurality of power receivers 4 having received these radio wavestransmits the receiving power information and the required electricenergy information. Accordingly, the power transmitter 3 can receive thereceiving power information and the required electric energy informationto calculate the transmission periods of the two or more powertransmission patterns 5 for use in the actual power transmission. Inthis way, adjusting the transmission periods of the two or more powertransmission patterns 5 allows the plurality of power receivers 4 toreceive the required electric energies within a predetermined time.

Second Embodiment

In the wireless power transmission device 1 according to the firstembodiment, each power receiver 4 transmits to the power transmitters 3the receiving power information per trial power transmission pattern forall of a plurality of trial power transmission patterns. However, as thenumber of trial power transmission patterns are larger, the number oftimes for each power receiver 4 to transmit the receiving powerinformation to the power transmitter 3 increases, so that the powerconsumption of each power receiver 4 increases. Essentially, it isdesirable that only the power receivers 4 for which feeding efficiencyby the trial power transmission patterns is high transmit the receivingpower information to the power transmitters 3. Accordingly, in thesecond embodiment, the power receivers 4 for which feeding efficiency bythe trial power transmission patterns is low are not allowed to transmitthe receiving power information to the power transmitter 3.

FIG. 14 is a block diagram illustrating a schematic configuration of awireless power transmission device 1 according to a second embodimentand illustrating a block configuration of a power transmitter 3. Thepower transmitter 3 illustrated in FIG. 14 has the same configuration asthe power transmitter 3 illustrated in FIG. 4, and further includes adetermination unit 31 and a transmission request unit 32.

The determination unit 31 determines per power receiver 4 whether thetransmission of receiving power information from a plurality of powerreceivers 4 is required, based on at least one of propagation pathinformation of the power receivers 4 and arrangement information of thepower receivers 4, and on power transmission pattern information to thepower receivers 4. The transmission request unit 32 requests a powerreceiver 4 for which the transmission of receiving power information hasbeen determined as required by the determination unit 31 to transmit thereceiving power information and the required electric energy informationrequired by that power receiver 4.

As a specific procedure for the determination unit 31, two ways of afirst procedure and a second procedure are considered.

In the first procedure, it is determined per power receiver 4 whetherthe transmission of receiving power information and required electricenergy information from the plurality of power receivers 4 is required,based on a value obtained by multiplying the propagation pathinformation of the power receivers 4 and the power transmission patterninformation to the power receivers 4.

The power transmission pattern information to the plurality of powerreceivers 4 can be expressed with phase and amplitude information(weight) of radio waves input into a plurality of power transmissionantennas 11 of a power transmitter 3. It is defined that the powertransmission antennas 11 of the power transmitter 3 are a phased arrayantenna having M elements in total and an m-th component (m=1 . . . M)of a propagation path vector to an n-th (n=1 . . . N) power receiver 4among N power receivers 4 in total is h_(n,m) which corresponds to apropagation path coefficient between the n-th power receiver 4 and them-th element of the phased array antenna. It is also defined that them-th component of a weight corresponding to a k-th power transmissionpattern is w_(k,m) which corresponds to phase and amplitude informationof radio waves input into the m-th element of the phased array antenna.A complex correlation coefficient ρ_(n,k) of a weight corresponding tothe propagation path vector and the k-th power transmission pattern tothe n-th power receiver 4 are expressed by the following equation (13):

$\begin{matrix}{\rho_{n,k} = \frac{\sum\limits_{m = 1}^{M}{h_{n,m}w_{k,m}}}{\sqrt{\sum\limits_{m = 1}^{M}{h_{n,m}}^{2}}\sqrt{\sum\limits_{m = 1}^{M}{w_{k,m}}^{2}}}} & (13)\end{matrix}$

In estimation of correlation, a value obtained by squaring the absolutevale of the complex correlation coefficient ρ_(n,k) expressed by theequation (13) is often used. When |ρ_(n,k)|² is equal to or larger thana predetermined value, it is determined that the transmission ofreceiving power information from a power receiver 4 is required. Ingeneral, in the case that |ρ_(n,k)|² is equal to or larger than 0.5, itis determined that the correlation is high. Therefore, the predeterminedvalue may be 0.5 or another value.

In the second procedure, the determination unit 31 determines per powerreceiver 4 whether the transmission of receiving power information andrequired electric energy information from the plurality of powerreceivers 4 are required, based on the arrangement information of thepower receivers 4 and the power transmission pattern information to thepower receivers 4. The arrangement information (relative positioninformation) of the power receivers 4 can be acquired from a camera,GPS, radar, etc. as described above. The power transmission patterninformation includes, for example, as illustrated in FIG. 15,information on a main beam direction (main robe) and a beam width of apower transmission pattern. The determination unit 31 compares therelative position information of the power receivers 4 and the main beamdirection and beam width of the power transmission pattern to determinewhether the power receivers 4 are located within the main beam range ofthe power transmission pattern. For the predetermined beam width, forexample, an angular width having 3 dB reduced from the maximum gain,so-called a half-value angle, may be employed. The power receivers 4located within the main beam range of the power transmission pattern isdetermined that the transmission of receiving power information isrequired.

Although the main beam direction and beam width of the powertransmission pattern can be acquired by preliminary measurements, it ispractically impossible to perform the measurements to all of assumedpower transmission patterns. Therefore, values calculated withsimulation may be used as the main beam direction and beam width of thepower transmission pattern. As for the simulation, it is not alwaysnecessary to use an electromagnetic field simulator. Those values can becalculated by a general-purpose computer based on directivity (alsoreferred to as an element factor) of a single antenna used as eachelement of the phased array antenna and arrangement coordinatesinformation and weight information (also referred to as an array factor)of each element of the phased array antenna.

In the above description, the procedure for determining whether thetransmission of receiving power information from each power receiver 4is required has been described. However, a power transmission pattern bywhich a group of predetermined two or more power receivers 4 satisfies apredetermined determination criterion may be decided and transmitted tothe group of power receivers 4. As for the classification to groups ofpower receivers 4, by using various clustering methods with variablessuch as a complex correlation coefficient between propagation pathvectors of two power receivers 4 obtained by the equation (13) andcoordinates information (for example, x-, y-, z-coordinates in theorthogonal coordinates) of each power receiver 4, the power receivers 4can be classified into a plurality of power receiver groups of powerreceivers 4 that have “a high correlation” with each other or that are“physically close” to each other. As typical clustering methods, Ward'smethod as a hierarchical method, K-means clustering as a nonhierarchicalmethod, etc. are listed.

Then, for example, as described above, a power transmission pattern canbe nominated based on weights (especially, a weight corresponding to themaximum singular value) obtained by singular value decomposition of apropagation path matrix to a plurality of power receivers 4 in eachgroup of power receivers 4.

FIG. 16 is a flowchart illustrating a procedure for the powertransmitter 3 according to the second embodiment. This flowchartillustrates a procedure for a batch feedback method similar to that ofFIG. 6. First, propagation path information of each power receiver 4 isacquired (step S21). Here, for example, a beacon signal transmitted fromeach power receiver 4 is received and, in the propagation pathestimation unit 18 of the power transmitter 3, propagation pathinformation between the power transmitter 3 to each power receiver 4 isestimated.

Next, it is determined by the determination unit 31 whether thetransmission of receiving power information from each power receiver 4is required (step S22). Here, in the above-described first or secondprocedure, it is determined whether the transmission of receiving powerinformation from each power receiver 4 is required.

Next, to the power receiver 4 which is determined as requiring thetransmission of receiving power information, the transmission ofreceiving power information and required electric energy information isnotified (step S23). This notification is made, for example, via thefirst communication unit 14.

Thereafter, similar to steps S1 to S7 of FIG. 6, the trial powertransmission, the reception of receiving power information and requiredelectric energy information, and the actual power transmission areperformed one by one (steps S24 to S30). When the sequential feedbackmethod is employed, in steps S24 to S30 of FIG. 16, steps S11 to S17 ofFIG. 8 are performed.

As described above, in the second embodiment, based on at least one ofthe propagation path information of the plurality of power receivers 4and the arrangement information of the power receivers 4, and the powertransmission pattern information to the power receivers 4, whether thetransmission of receiving power information from the power receivers 4is required is determined per power receiver 4. Accordingly, it isenough that, per power transmission pattern, only the power receivers 4for which feeding efficiency is high transmit the receiving powerinformation and the required electric energy information to the powertransmitter 3, so that the power consumption of each power receiver 4 isreduced and the number of pieces of information such as the receivingpower information to be received by the power transmitter 3 is alsoreduced, and hence the processing load of the power transmitter 3 can bedecreased.

The procedure for each component in the power transmitter 3 according toeach of the above-described embodiments can be executed by one or moresignal processors. Moreover, the power transmitter 3 may be configuredwith SoC (System on Chip) having one or more signal processors andmemories integrated together.

At least part of the wireless power transmission devices 1 and thewireless power transmission system 2 described above in relation to theembodiment may be formed by hardware or software. In the case of formingby software, programs for implementing the functions of at least some ofthe wireless power transmission devices 1 and the wireless powertransmission system 2 may be stored in a recording medium such as aflexible disc or a CD-ROM and read and executed by a computer. Therecording medium is not limited to a detachable one such as a magneticdisc or an optical disc but may be a fixed recording medium such as ahard disc device or a memory.

In addition, the programs for implementing the functions of at leastpart of the wireless power transmission devices 1 and the wireless powertransmission system 2 may be distributed via a communication line suchas the internet (including wireless communication). Further, theprograms may be distributed via a wired line or a wireless line such asthe internet or through a recording medium in an encrypted, modulated,or compressed state.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1. A wireless power transmission device that transmits wireless power bya radio wave to a plurality of power receivers, comprising: a powertransmission condition calculator that calculates power transmissionconditions including power transmission periods of two or more of aplurality of different power transmission patterns based on receivingpower information and required electric energy information from theplurality of power receivers; and power transmission circuitry thattransmits a radio wave while switching between the two or more powertransmission patterns under the calculated power transmissionconditions.
 2. The wireless power transmission device according to claim1, wherein the power transmission conditions include the powertransmission periods of the two or more power transmission patterns andat least one of directions of the two or more power transmissionpatterns, phase of the radio wave, and amplitude of the radio wave. 3.The wireless power transmission device according to claim 1, furthercomprising: a first controller that controls trial power transmission ofradio waves based on the plurality of power transmission patterns insequence from the power transmission circuitry; and a first communicatorthat receives the receiving power information and the required electricenergy information transmitted from the plurality of power receivershaving received the radio waves, wherein the power transmissioncondition calculator calculates the power transmission conditions basedon the receiving power information and the required electric energyinformation received by the first communicator.
 4. The wireless powertransmission device according to claim 1, wherein the power transmissioncondition calculator calculates the power transmission conditions suchthat wireless power meeting required electric energies of the pluralityof power receivers is transmitted to the plurality of power receiverswithin a predetermined time.
 5. The wireless power transmission deviceaccording to claim 1, wherein the power transmission circuitry dividesthe power transmission periods of the plurality of power transmissionpatterns calculated by the power transmission condition calculator intoa plurality of power transmission division periods and transmits powerwhile switching between the kinds of the power transmission patterns inthe individual power transmission division periods.
 6. The wirelesspower transmission device according to claim 1, further comprising aphased array antenna that has a plurality of antennas that transmits orreceives a radio wave to or from the plurality of power receivers and avariable phase shifter that is connected to the plurality of antennas tocontrol variably phase of the radio wave to generate the plurality ofpower transmission patterns.
 7. The wireless power transmission deviceaccording to claim 1, wherein the radio wave transmitted by the powertransmission circuitry under the calculated power transmissionconditions is a non-modulated continuous wave, and frequency of theradio wave transmitted by the power transmission circuitry under thecalculated power transmission conditions is different from frequency ofa radio wave for the plurality of power receivers to transmit thereceiving power information and the required electric energyinformation.
 8. The wireless power transmission device according toclaim 1, further comprising a propagation path estimator that estimatesa propagation path between each of the plurality of power receivers andthe wireless power transmission device, wherein at least one of the twoor more power transmission patterns for which the power transmissionconditions are calculated by the power transmission condition calculatoris generated based on the propagation path estimated by the propagationpath estimator.
 9. The wireless power transmission device according toclaim 1, further comprising power receiver localization circuitry thatdetects at least one of locations and directions of the plurality ofpower receivers, wherein at least one of the two or more powertransmission patterns for which the power transmission conditions arecalculated by the power transmission condition calculator is generatedbased on at least one of the locations and directions of the pluralityof power receivers.
 10. A wireless power transmission device thattransmits wireless power by a radio wave to a plurality of powerreceivers, comprising: a determination unit that determines whetherreceiving power information from the plurality of power receivers isrequired based on at least one of propagation path information of theplurality of power receivers and arrangement information of theplurality of power receivers, and power transmission pattern informationto the plurality of power receivers; a transmission request unit thatrequests a power receiver for which the receiving power information isdetermined as required by the determination unit to transmit thereceiving power information and required electric energy informationrequired by the power receiver; a power transmission conditioncalculator that calculates power transmission conditions including powertransmission periods of two or more of a plurality of different powertransmission patterns based on the receiving power information and therequired electric energy information from a power receiver havingaccepted a request from the transmission request unit; and powertransmission circuitry that transmits a radio wave while switchingbetween the two or more power transmission patterns under the calculatedpower transmission conditions.
 11. The wireless power transmissiondevice according to claim 10, wherein the determination unit determinesper power receiver whether the receiving power information and therequired electric energy information from the plurality of powerreceivers are required based on a value obtained by multiplying thepropagation path information from the plurality of power receivers andthe power transmission pattern information to the plurality of powerreceivers.
 12. The wireless power transmission device according to claim10, wherein the determination unit determines per power receiver whetherthe receiving power information and the required electric energyinformation from the plurality of power receivers are required based onthe arrangement information of the plurality of power receivers and thepower transmission pattern information to the plurality of powerreceivers.
 13. The wireless power transmission device according to claim10, wherein the power transmission conditions include the powertransmission periods of the two or more power transmission patterns andat least one of directions of the two or more power transmissionpatterns, phase of the radio wave, and amplitude of the radio wave. 14.The wireless power transmission device according to claim 10, furthercomprising: a first controller that controls trial power transmission ofradio waves based on the plurality of power transmission patterns insequence from the power transmission circuitry; and a first communicatorthat receives the receiving power information and the required electricenergy information transmitted from at least one of the plurality ofpower receivers having received the radio waves, wherein the powertransmission condition calculator calculates the power transmissionconditions based on the receiving power information and the requiredelectric energy information received by the first communicator.
 15. Thewireless power transmission device according to claim 10, wherein thepower transmission condition calculator calculates the powertransmission conditions such that wireless power meeting requiredelectric energies required by each power receiver is transmitted to acorresponding power receiver within a predetermined time.
 16. Thewireless power transmission device according to claim 10, wherein thepower transmission circuitry divides each power transmission period ofthe two or more power transmission patterns calculated by the powertransmission condition calculator into a plurality of power transmissiondivision periods and transmits power while switching between the kindsof the power transmission patterns in the individual power transmissiondivision periods.
 17. The wireless power transmission device accordingto claim 10, further comprising a phased array antenna that has aplurality of antennas that transmits or receives a radio wave to or fromthe plurality of power receivers and a variable phase shifter that isconnected to the plurality of antennas to control variably phase of theradio wave to generate the plurality of power transmission patterns. 18.A wireless power transmission system comprising: one or more powertransmitters; and a plurality of power receivers that receives wirelesspower by a radio wave transmitted from the one or more powertransmitters, wherein each of the one or more power transmitterscomprises: a power transmission controller that controls for performingtrial power transmission of a plurality of radio waves based on aplurality of power transmission patterns in sequence from the powertransmitter; first communicator that receives receiving powerinformation and required electric energy information transmitted fromthe plurality of power receivers having received the plurality of radiowaves; a first calculator that calculates power transmission conditionsincluding power transmission periods of two or more of a plurality ofdifferent power transmission patterns based on the receiving powerinformation and the required electric energy information from theplurality of power receivers; and power transmission circuitry thattransmits the radio wave while switching between the two or more powertransmission patterns under the calculated power transmissionconditions, wherein each of the plurality of power receivers comprises:power reception circuitry that receives the radio wave transmitted fromthe power transmission circuitry and generates direct-current power; asecond calculator that, when the power reception circuitry receives theradio waves based on the plurality of power transmission patternstransmitted in trial power transmission from any of the one or morepower transmitters, calculates receiving power information of thereceived radio waves; and a second communicator that transmits a radiowave including the receiving power information and the required electricenergy information.
 19. The wireless power transmission system accordingto claim 18, wherein the second communicator in at least one of theplurality of power receivers transmits a beacon signal before the one ormore power transmitters perform the trial power transmission, at leastone of the one or more power transmitters comprises a propagation pathestimator that, based on the beacon signal received by the firstcommunicator, estimates propagation path information with the powerreceiver having transmitted the beacon signal, and at least one of thetwo or more power transmission patterns for which the power transmissionconditions are calculated by the power transmission condition calculatoris generated based on the propagation path information.
 20. A wirelesspower transmission device comprising: a power reception circuitry thatreceives a radio wave from one or more power transmitters and generatesdirect-current power; a receiving power generator that, when radio wavesbased on a plurality of power transmission patterns transmitted in trialpower transmission from any of the one or more power transmitters isreceived by the power reception circuitry, generates receiving powerinformation of the received radio waves; and a communicator thattransmits the receiving power information and required electric energyinformation, wherein the power reception circuitry generates thedirect-current power based on a radio wave while switching between twoor more of the plurality of power transmission patterns transmitted fromthe power transmitter having received the receiving power informationand the required electric energy information and received by the powerreception circuitry, in respective specific power transmission periods.